Subjects of research: polaron, bipolaron, cuprates.
Purpose of work: development of small polaron Holstein model, taking into account long-range electron-phonon interaction to establish the possible existence of a polaron with a small mass and explain the value of the mass of the charge carrier, infrared absorption, and the high values of the superconducting transition temperature in cuprate high-temperature superconductors.
Methods of research: method of secondary quantization, Lang-Firsov transformation, perturbation theory method, quasiclassical approach (WK.B method), Frank-Condon principle, nonadiabatic and adiabatic approaches.
The results obtained and their novelty: condensed matter theory, theory of strongly interacting system of electrons and phonons, in particular theory of lattice Holstein polarons with long-range electron-phonon interaction are developed. Besides that in the thesis a theory of pairing of two polarons is developed and a new theory of influence of external pressure (strain) on the temperature of Bose-Einstein condensation of lattice bipolarons is proposed.
Practical value: lies in the possibility of their use in general for the development of solid-state theory, the theory of interacting electron-phonon systems, in particular the Holstein’s lattice-polaron theory. In addition, from a practical point of view, the developed methods allow us to calculate the mass of the charge carrier in the cuprates, to calculate the optical conductivity of polarons, assess the conditions of existence of two-site bipolaron, and the superconducting transition temperature based on the bipolaron model of superconductivity.
Degree of embed and economic effectivity: The work is fundamental and its results can be used for theoretical interpretation of experimental data on the effective mass of carriers in the cuprates, the optical (IR) absorption of the cuprates, the order parameter of superconductivity in cuprates and in experiments on the effect of external pressure (strain) at superconducting transition temperature of cuprates.
Field of application: condensed matter physics and high temperature superconducting material science.
